二叉树的创建、先序、中序、后序、层序的递归与非递归算法(java)

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二叉树的创建、四种遍历算法递归与非递归
package ccnu.offer.tree;import java.util.ArrayList;import java.util.LinkedList;import java.util.Scanner;import java.util.Stack;public class Demo02 {    public static void main(String[] args) {        Demo02 d = new Demo02();//      Node root = d.createBiTree();//      d.preOrder(root);        Node root1 = d.createBiTreeByPreIn(new int[]{1, 2, 4, 6, 7, 3, 5, 8, 9}, new int[]{2, 6, 4, 7, 1, 5, 9, 8, 3}, 0, 0, 9); // postSerials = [6, 7, 4, 2, 9, 8, 5, 3, 1]//      Node root1 = d.createBiTreeByPreIn(new int[]{1, 2, 4, 5, 3, 6, 7}, new int[]{4, 2, 5, 1, 3, 7, 6}, 0, 0, 7); // postSerials = [6, 7, 4, 2, 9, 8, 5, 3, 1]//      Node root1 = d.createBiTreeByPreIn(new int[]{1, 2, 3, 4, 5}, new int[]{2, 1, 4, 3, 5}, 0, 0, 5); // postSerials = [6, 7, 4, 2, 9, 8, 5, 3, 1]//      d.preOrder(root1);        System.out.println(d.preOrder1(root1));        System.out.println(d.inOrder1(root1));        System.out.println(d.postOrder1(root1));//      System.out.println(d.postOrder2(root1));        System.out.println(d.levelOrder(root1));        System.out.println(d.levelOrder1(root1));        /*ArrayList<Integer> levelSerials = d.levelOrder(root1);        for(Integer levelSerial : levelSerials){            if(levelSerial == -1){                System.out.println();            }else{                System.out.print(levelSerial);            }        }*/    }    public Node createBiTree(){        Scanner sc = new Scanner(System.in);        int val;        Node root;        val = sc.nextInt();        if(val == -1){            return null;        }else{            root = new Node(val);            root.lchild = createBiTree();            root.rchild = createBiTree();        }        return root;    }    public Node createBiTreeByPreIn(int[] pre, int[] in, int preBegin, int inBegin, int len){        if(pre == null || in == null || pre.length != in.length || pre.length == 0 || in.length == 0){            return null;        }        if(len <= 0){            return null;        }        Node root = new Node(pre[preBegin]);        int rootIndex;        for(rootIndex = 0; in[rootIndex] != pre[preBegin]; rootIndex++);        root.lchild = createBiTreeByPreIn(pre, in, preBegin + 1, inBegin, rootIndex - inBegin);        root.rchild = createBiTreeByPreIn(pre, in, preBegin + (rootIndex - inBegin) + 1, rootIndex + 1, len - (rootIndex - inBegin) - 1);        return root;    }    public void preOrder(Node root){ // 递归        if(root != null){            System.out.print(root.val);            preOrder(root.lchild);            preOrder(root.rchild);        }    }    public ArrayList<Integer> preOrder1(Node root){ // 非递归        ArrayList<Integer> preSerials = new ArrayList<Integer>();        Stack<Node> s = new Stack<Node>();        while(root != null || !s.isEmpty()){            if(root != null){                preSerials.add(root.val);                s.push(root);                root = root.lchild;            }else{                root = s.pop();                root = root.rchild;            }        }        return preSerials;    }    public void inOrder(Node root){ // 递归        if(root != null){            inOrder(root.lchild);            System.out.print(root.val);            inOrder(root.rchild);        }    }    public ArrayList<Integer> inOrder1(Node root){ // 非递归        ArrayList<Integer> inSerials = new ArrayList<Integer>();        Stack<Node> s = new Stack<Node>();        while(root != null || !s.isEmpty()){ // 当整棵树根节点被访问时，此时栈为空，接着访问根节点的右子树，而当某个树root的左子树为空时，栈一定不为空，应为root在栈顶----!s.isEmpty()就是访问当前根节点(栈顶元素)            if(root != null){ // 当前树的root不为空，将其入栈，并将root重新指向其左子树                s.push(root);                root = root.lchild;            }else{ // 当root为空时,说明其父节点(栈顶元素)的左孩子为空，则应该访问，继而在将root指向栈顶元素的右子树                root = s.pop();                inSerials.add(root.val);                root = root.rchild;            }        }        return inSerials;    }    public void postOrder(Node root){ // 递归        if(root != null){            postOrder(root.lchild);            postOrder(root.rchild);            System.out.print(root.val);        }    }    public ArrayList<Integer> postOrder1(Node root){ // 非递归        ArrayList<Integer> postSerials = new ArrayList<Integer>();        Stack<Node> s = new Stack<Node>();        Node isAccess = null; // 记录最近的访问节点        while(root != null || !s.isEmpty()){            if(root != null){                s.push(root);                root = root.lchild;            }else{ // 某棵子树木有左子树                root = s.peek();                root = root.rchild;                if(root == null || isAccess == root){ // 木有右子树或者右子树已经被访问，那么就可以访问访问栈顶元素(左右子树均已访问)                    root = s.pop();                    postSerials.add(root.val);                    isAccess = root; // 记录刚访问的这个节点                    root = null; // 刚访问的root的左右子树均已经访问(root也访问了)，此时应该从获取栈顶元素(root的父节点)，遍历父节点的右子树                }else{                    s.push(root);                    root = root.lchild;                }            }        }        return postSerials;    }     public ArrayList<Integer> postOrder2(Node root) {        ArrayList<Integer> postSerials = new ArrayList<Integer>();        ArrayList<Integer> leftPostSerials = new ArrayList<Integer>();        ArrayList<Integer> rightPostSerials = new ArrayList<Integer>();        if (root == null) {            return postSerials;        }        leftPostSerials = postOrder2(root.lchild);        rightPostSerials = postOrder2(root.rchild);        postSerials.addAll(leftPostSerials);        postSerials.addAll(rightPostSerials);        postSerials.add(root.val);        return postSerials;    }    public ArrayList<Integer> levelOrder(Node root){ // 自上而下，自左向右        int levels = 0; // 记录二叉树的层数        ArrayList<Integer> levelSerials = new ArrayList<Integer>();        LinkedList<Node> levelNodes = new LinkedList<Node>();        Node rightmost1 = null; // 始终指向正在访问的当前层的最右一个节点        Node rightmost2 = null; // 始终指向正在访问的当前层的当前节点的最右一个节点        while(root != null || !levelNodes.isEmpty()){            if(root != null){ // 初始化第一个节点                levelNodes.push(root);                rightmost1 = root;                rightmost2 = root;                root = null;            }else{                root = levelNodes.pop();                levelSerials.add(root.val);                if(root.lchild != null){                    levelNodes.addLast(root.lchild);                    rightmost2 = root.lchild;                }                if(root.rchild != null){                    levelNodes.addLast(root.rchild);                    rightmost2 = root.rchild;                }                if(root == rightmost1){                    levels++;                    levelSerials.add(-1); // 表示此处是此层的最后一个节点                    rightmost1 = rightmost2;                }                root = null;            }        }    System.out.println("levels: " + levels);        return levelSerials;    }    public ArrayList<Integer> levelOrder1(Node root){ // 自下而上，自右向左        ArrayList<Integer> levelSerials = new ArrayList<Integer>();        LinkedList<Node> levelNodes = new LinkedList<Node>();        Stack<Node> accessNodes = new Stack<Node>();        Node rightmost1 = null;        Node rightmost2 = null;        while(root != null || !levelNodes.isEmpty()){            if(root != null){                levelNodes.push(root);                rightmost1 = root;                rightmost2 = root;                root = null;            }else{                root = levelNodes.pop();                accessNodes.push(root);                if(root.lchild != null){                    levelNodes.addLast(root.lchild);                    rightmost2 = root.lchild;                }                if(root.rchild != null){                    levelNodes.addLast(root.rchild);                    rightmost2 = root.rchild;                }                if(root == rightmost1){                    accessNodes.push(new Node(-1)); // 标志下一层的额外节点                    rightmost1 = rightmost2;                }                root = null;            }        }        while(!accessNodes.isEmpty()){            levelSerials.add(accessNodes.pop().val);        }        return levelSerials;        }    private class Node{        private int val;        private Node lchild = null;        private Node rchild = null;        public Node(int val) {            this.val = val;        }    }}
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